Containers for storage and administration of medical solutions are well known. Such containers are commonly referred to as partial additive bags or PABs. One such container is disclosed in U.S. Pat. No. 4,484,916 to McPhee, assigned to the present assignee. The container disclosed in the above-mentioned patent is formed of a plastic bag and a molded plastic header section. In the header section, there is an inlet port for admitting medication, nutrients, etc., into the bag, and an outlet port through which the bag's contents may be drawn for ultimate delivery to a patient.
The outlet port is a hollow, substantially cylindrical structure sealed by an internal, pierceable diaphragm. Medication, typically in liquid form, is administered from the container to a patient through IV tubing coupled to the container by means of a filter spike. The combination of IV tubing and spike are usually referred to as "an administration set." The spike, usually formed of a hollow, cylindrical shaft terminated by a tapered tip, is pushed into the outlet port so that the tip pierces the diaphragm. As insertion continues, the spike's cylindrical shaft spreads the diaphragm open as it passes through. During insertion and thereafter, the diaphragm frictionally engages the spike, forming a seal between the diaphragm and the spike to prevent the loss of liquids or air from the bag around the spike's exterior. After the spike is fully inserted, the bag can be turned upside down with the outlet port on the bottom, so that the medical solution can pass through the hollow spike to the IV tubing and, ultimately, to the patient. Frictional engagement between the spike and diaphragm helps to secure the spike in the outlet port.
It is conventional to form the pierceable diaphragm of the above-described outlet port in a plane normal to the axis of the port and, hence, normal to the insertion direction of the spike. However, it has been discovered that the force required to fully insert the spike increases sharply to an undesirably high level at the point where the cylindrical shaft of the spike engages the diaphragm. This sharp increase in resistance to pushing the spike through the diaphragm can be mistaken for the point of full insertion, so that the person discontinues the insertion process. When such a spike is not fully inserted, leakage can occur. Moreover, if insertion falls short of where the cylindrical portion of the spike's shaft fully engages and bears against the ruptured diaphragm, there is a danger that, when the container is suspended upside-down, the spike will slip out of the port, since a substantial part of the force retaining the spike in the port is due to the frictional engagement between spike and diaphragm. Incomplete spike penetration will thus result in waste of fluid, or even waste of the container, and possible contamination of the spike.
These problems are exacerbated by the use of different-diameter spikes. Generally, the greater the diameter of the spike, the greater the penetration force required. Spikes normally range from 3/16-inch to 1/4-inch in diameter at the cylindrical portion, with the penetration force needed for the 1/4-inch spike being significantly greater than that for the 3/16-inch spike.
One way to reduce the required penetration force is to decrease the thickness of the diaphragm or to weaken the material of the diaphragm, or both. However, this reduces the reliability of the seal created by the diaphragm and can reduce the retention force on a spike which has been inserted. Another way to reduce the insertion force is to increase the diameter of the outlet port with respect to the spike, but this also reduces the retention force. Accordingly, it is difficult to design a port whose diaphragm is more easily penetrable by a spike without also unacceptably reducing the force required to withdraw the spike from the port.